I have a 1991 300D 2.5, that really does not heat that well. After doing a search on this board, I found lots of information about the mono-valve, but I still have some questions.
1. What exactly, in detail does the mono-valve do?
2. Why would a bad monovalve give me limited heat?
3. What exactly does it look like? Is it electrical, mechanical, or other?
4. How do you replace it? Where is it located? Any special tools needed?

Thanks for your help,
Sincerely,
Cold in Maryland